As differential devices for vehicles, there are widely employed differential devices with a limited-slip differential mechanism configured to, even when one wheel on the vehicle is lifted and run idle, transfer sufficient torque to the other wheel via a clutch means to prevent, situations in which, when the one wheel rises up over ice, snow, or mud, for example, and runs idle, sufficient torque is not transferred to the other wheel to disable the vehicle to be started, or in which the vehicle fishtails during cornering or at sudden starting or the like.
For example, Patent Documents 1 and 2 each disclose a differential device 100 with a limited-slip differential mechanism as shown in FIG. 15. The differential device 100 includes: a pair of pressure rings 103 that is provided in a differential case 101 so as to be capable of movement along axles 102 and incapable of relative rotation; a pinion shaft 101 that is orthogonal to the axles 102 and held at shaft end between the pressure rings 103; a pinion gear 105 that is rotatably provided at the pinion shaft 104; a pair of side gears 106 that are provided at axle ends of the right and left axles 102 so as to be incapable of relative rotation, and that engage with the pinion gear 105 on both sides of the pinion gear 105; an operation means 108 that operates the pressure rings 103 in a direction in which a clearance 107 increases between the pressure rings 103 with increase in relative rotation torque between the pinion shaft 104 and the differential case 101 with a differential; and clutch means 109 that are disposed on both sides of a pair of the pressure rings 103 along the axles and are operated by the pressure rings 103 to limit a differential between the right and left axles 102 with increase in the clearance 107.
The operation means 108 is suggested in various shapes. In the employed operation means 108, for example, square cam parts 110 are formed at shaft ends of the pinion shaft 104 so as to have one diagonal line positioned along the axles, and almost V-shaped cam grooves 111 are formed in the pressure rings 103 to engage the cam parts 110.
In the differential device 100, when relative, rotation torque is generated between the pinion shaft 104 and the differential case 101 and the operation means 108 makes the clearance, 107 increase between the pressure rings 103, the clutch means 109 are activated to limit, a differential between the right and left wheels. To return the clearance 107 in the both pressure rings 103 to the set amount in the normal state, elastic members 112 such as disc springs are disposed on outer sides of the both clutch means 109 along the axles to bias the pressure springs 103 to come closer to each other via a plurality of clutch plates 113 in the clutch means 109.
Since the elastic members 112 in the differential device 100 bias the pressure rings 103 to come closer to each other via the clutch plates 113, when the biasing force of the elastic members 112 is made weak, the clutch means 109 are operated more easily by the operation means 108, and thus the vehicle may enter into a differential-limited state even during low-speed cornering, thereby resulting in an unstable differential state. Meanwhile, when the biasing force of the elastic members 112 is made strong, the operation means 108 enters into a differential state. However, the clutch plates 113 are constantly in friction pressure contact by the biasing force of the elastic members 112 to bring virtually the operation means 108 into a differential-limited state, and eventually it is not possible to provide the stable differential state during low-speed cornering. Accordingly, the vehicle cannot turn in a small radius during low-speed cornering, or the vehicle exhibits a so-called chattering phenomenon in which the differential-limited state and the differential state are switched back and forth to deteriorate maneuverability of the vehicle or exert adverse influence on the differential device 100 and peripheral devices thereof by the impact of chattering.
Accordingly, the applicant has suggested and put into practical use a differential device with a limited-slip differential mechanism configured to switch appropriately between the differential state and the differential-limited state, by providing biasing means to bias the pressure rings to come closer to each other, not through the clutch plates, to omit the elastic members 112 or provide the elastic members 112 with biasing force weakened to such an extent that play of the clutch plates is removed, as disclosed in Patent Document 3.